Machines for feeding and completing partially formed and filled, top-loaded paperboard cartons are well-known in the art. For many years, the most efficient approach for the high speed feeding and forming of such cartons, including closing the lid and sealing the corresponding flaps, was a continuous or in-line one. An early example of this approach is found in commonly assigned U.S. Pat. No. 3,267,637 to Baker, which is incorporated herein by reference. The machine disclosed in this patent uses fixedly mounted, upstanding lugs or “pushers” carried by spaced parallel chains to convey the carton. Specifically, after folding of the lid and pre-folding of the trailing end flap, the carton is pushed along by the lugs while the front flap on the lid is simultaneously folded and sealed. Pushing from the trailing end of the carton advantageously helps to maintain the lid in the proper registration during folding and sealing of the front flap. To efficiently fold the opposite side flaps, the carton with the folded and partially sealed lid is then turned about its vertical axis while forward feeding continues. After turning, the carton is conveyed in-line by upstanding lugs of a downstream conveyor while the side flaps are sealed, thus completing the carton.
A more modern “lugless” example of the continuous carton forming approach is found in commonly assigned U.S. Pat. No. 5,660,262 to Landrum et al., the disclosure of which is also incorporated herein by reference. In this approach, infeed belts frictionally engage the top and bottom surfaces of the carton for conveying while the front flap is sealed. This avoids the need for pre-folding the trailing end flap, as is required when conveying using upstanding lugs to avoid damaging it during feeding. After the front flap is sealed, the carton enters a zone including a plurality of spaced parallel belts running at different speeds complete the turning through 90°. The turned carton is then received and conveyed by spaced belts while the opposite side flaps are folded and sealed. The carton is thus formed in a continuous fashion without stopping or changing the conveying direction.
While these continuous or in-line approaches have enjoyed considerable commercial success, there are certain disadvantages. For example, running plural spaced belts at different speeds to turn the carton during feeding increases the complexity of the machine. Moreover, to achieve turning through 90 degrees while continuously conveying the carton, the machine must have a relatively great longitudinal dimension. This requirement can present difficulties where floor space is limited. Maintenance costs are also increased in view of the need for ensuring that the differential speeds of the belts are in the proper relationship for turning the carton in the desired fashion. In the modern approach using spaced top and bottom running belts to feed the carton while the front flap is sealed, the differential force created on the opposite surfaces of the carton must also be kept in check, as it can lead to mis-registration of the lid or closure. The problem with mis-registration is especially prevalent during high speed conveying, which of course is a desirable mode of operation to maximize productivity.
As suggested above, others in the past have solved the mis-registration problem by employing spaced conveyors with fixed, upstanding lugs for engaging and pushing the carton from along the trailing end. In this arrangement, the conveyor speed is selected to ensure that the upstanding lugs reach the trailing end of the carton at the desired instant in time. The Baker '637 patent is representative of this approach. However, the more modern types of “pusher” conveyors include selectively extendable lugs capable of moving from a retracted position to an actuated position for engaging and conveying the carton. In either case, pushing a top-loaded carton from along the trailing end using lugs helps to avoid problems with mis-registration of the lid or closure. Consequently, keeping the carton conveying speed in check may be unnecessary using this type of arrangement.
Although the use of extensible lugs solves the timing problems created by fixed lugs and the mis-registration problems that may result from using of spaced belt conveyors, all known prior approaches employ lugs attached to the associated chain at fixed intervals generally selected to correspond to the length of the cartons in the conveying direction. This lug-to-lug spacing serves as a significant limitation on the operating speed or throughput of the machine. This is because, unless the actuated lug reaches the trailing end of the carton at the exact instant it is introduced to the machine, a significant delay may occur while this lug catches up (or the next-in-line lug actuated reaches the carton, in the case where the preceding actuated lug has already passed). In relative terms, this resulting delay may be substantial, especially when the length of the carton in the conveying direction only slightly exceeds the fixed pitch distance of the lugs. This problem could possibly be resolved by precisely timing the feeding of the cartons to the machine, but this complicates matters and does not allow for use in an arrangement where the carton feed is random.
Additionally, past and current mechanisms used to actuate extensible lugs are somewhat obtuse and inefficient. In the usual case, the lug is immediately extended in the conveying path in a single movement and retracted in this same fashion. As a result, it often interferes with the proper conveyance of the cartons, and dictates maintaining certain spacing requirements (which deleteriously either decreases the throughput or increases the footprint/size of the machine). Once pivoted, the lugs also lock in the actuated position and a pivot block, cam or like structure is required to actively engage and return the actuated lug to the retracted position. This requirement adds to the overall complexity, which directly correlates to both the manufacturing and maintenance costs.
Accordingly, a need exists for an improved carton feeding and forming machine that overcomes the foregoing limitations and others. A need is also identified for an improved conveyor with selectively actuated lugs having a small “pitch” (such as, for example, a center-to-center spacing less than the width of a lug in the conveying direction). A selected one of such closely spaced lugs could be actuated at a desired instant in time for engaging a carton or other object, thus making such an arrangement better adapted for use in conveying cartons of varying lengths or introduced in a random fashion. As will be demonstrated herein, the use of such lugs in a carton feeding and forming machine would provide a number of benefits, including but not limited to a vast improvement in efficiency, reliability, and accuracy of the operation with a concomitant reduction in operating and maintenance costs.